A semiconductor dynamic quantity sensor such as that disclosed in, for example, JP-A-11-326365, is a differential capacitance type comprising first fixed electrodes and second fixed electrodes opposed to movable electrodes, to detect an applied dynamic quantity based on a change in the differential capacitance between a capacitance by the movable electrodes and first fixed electrodes and a capacitance by the movable electrodes and second fixed electrodes, that accompany the displacement of the movable electrodes when the dynamic quantity is applied.
In this semiconductor dynamic quantity sensor, a silicon substrate on the lower side of an SOI (silicon-on-insulator) is used as a support substrate, and trenches are formed in the silicon substrate on the upper side by trench etching to thereby form movable electrodes and fixed electrodes as well as peripheral fixed portions for the electrodes.
More fully, the semiconductor dynamic quantity sensor of the differential capacitance type comprises a peripheral fixed portion fixed and supported on the support substrate along the peripheral portion of the support substrate, movable electrodes supported on the support substrate on the inside of the peripheral fixed portion and displaceable in a horizontal direction relative to the substrate surface, and first fixed electrodes and second fixed electrodes fixed and supported on the support substrate on the inside of the peripheral fixed portion and that are opposed to the movable electrodes via a detection gap.
A first capacitance CS1 is formed between the movable electrodes and the first fixed electrodes, and a second capacitance CS2 is formed between the movable electrodes and the second fixed electrodes, to detect the applied dynamic quantity based on a change in the differential capacitance between the first capacitance CS1 and the second capacitance CS2, that accompanies the displacement of the movable electrodes when the dynamic quantity is applied.
Therefore, the semiconductor dynamic quantity sensor of this kind is inspected to determine if the detector capacitance portion between the movable electrodes and the fixed electrodes is normally working.
Namely, the movable electrodes undergo the displacement in a horizontal direction relative to the surface of the substrate upon the application of a dynamic quantity, whereby the distance varies between the movable electrodes and the fixed electrodes accompanying the displacement and, therefore, the capacitance varies. Here, when a given dynamic quantity is applied, it is inspected to determine if a desired change in the capacitance is obtained.
Here, in the above semiconductor dynamic quantity sensor in which the movable electrodes are provided on the support substrate so as to be opposed thereto in a separated manner, it is necessary to perform an inspection to determine if the movable electrodes are normally displacing in a direction perpendicular to the surface of the substrate accompanying the application of a dynamic quantity.
If, for example, a foreign matter exists between the movable electrodes and the support substrate, the movable electrodes displace in the direction of the support substrate upon the application of a dynamic quantity in a direction perpendicular to the surface of the substrate, and come into contact with the foreign matter resulting in an abnormal displacement.
In the semiconductor dynamic quantity sensor, usually, a dedicated electrode is separately formed to give a potential to the support substrate so as to form the potential of the support substrate in order to inspect any abnormal displacement of the movable electrodes in the direction perpendicular to the surface of the substrate. In this case, the inspection is made possible by the generation of an electrostatic attractive force due to a potential differential occurring between the support substrate and the movable electrodes.
However, separately forming the dedicated electrode for giving a potential to the support substrate is cumbersome from the standpoint of production steps, and causes the constitution of the sensor to become complex.
The above problem is not specific to the semiconductor dynamic quantity sensor of the above differential capacitance type but is common to the semiconductor dynamic quantity sensors in which the peripheral fixed portion is provided on the support substrate, the movable electrodes and the fixed electrodes facing thereto are provided on the inside thereof, and the applied dynamic quantity is detected based on a change in the distances among the movable electrodes and the fixed electrodes when the dynamic quantity is applied.